Merge branch 'tb/weak-sha1-for-tail-sum'

The checksum at the tail of files are now computed without
collision detection protection.  This is safe as the consumer of
the information to protect itself from replay attacks checks for
hash collisions independently.

* tb/weak-sha1-for-tail-sum:
  csum-file.c: use unsafe SHA-1 implementation when available
  Makefile: allow specifying a SHA-1 for non-cryptographic uses
  hash.h: scaffolding for _unsafe hashing variants
  sha1: do not redefine `platform_SHA_CTX` and friends
  pack-objects: use finalize_object_file() to rename pack/idx/etc
  finalize_object_file(): implement collision check
  finalize_object_file(): refactor unlink_or_warn() placement
  finalize_object_file(): check for name collision before renaming

1 files changed, 25 insertions, 0 deletions

diff --git a/Makefile b/Makefile
index 7344a7f725..2dde1fd2b8 100644
--- a/Makefile
+++ b/Makefile
@@ -521,6 +521,10 @@ include shared.mak
 # Define APPLE_COMMON_CRYPTO_SHA1 to use Apple's CommonCrypto for
 # SHA-1.
 #
+# Define the same Makefile knobs as above, but suffixed with _UNSAFE to
+# use the corresponding implementations for unsafe SHA-1 hashing for
+# non-cryptographic purposes.
+#
 # If don't enable any of the *_SHA1 settings in this section, Git will
 # default to its built-in sha1collisiondetection library, which is a
 # collision-detecting sha1 This is slower, but may detect attempted
@@ -1997,6 +2001,27 @@ endif
 endif
 endif
 
+ifdef OPENSSL_SHA1_UNSAFE
+ifndef OPENSSL_SHA1
+	EXTLIBS += $(LIB_4_CRYPTO)
+	BASIC_CFLAGS += -DSHA1_OPENSSL_UNSAFE
+endif
+else
+ifdef BLK_SHA1_UNSAFE
+ifndef BLK_SHA1
+	LIB_OBJS += block-sha1/sha1.o
+	BASIC_CFLAGS += -DSHA1_BLK_UNSAFE
+endif
+else
+ifdef APPLE_COMMON_CRYPTO_SHA1_UNSAFE
+ifndef APPLE_COMMON_CRYPTO_SHA1
+	COMPAT_CFLAGS += -DCOMMON_DIGEST_FOR_OPENSSL
+	BASIC_CFLAGS += -DSHA1_APPLE_UNSAFE
+endif
+endif
+endif
+endif
+
 ifdef OPENSSL_SHA256
 	EXTLIBS += $(LIB_4_CRYPTO)
 	BASIC_CFLAGS += -DSHA256_OPENSSL